Long‐term humoral immunity decline in hemodialysis patients following severe acute respiratory syndrome coronavirus 2 vaccination: A cohort study

Abstract Background and Aims Dialysis patients are extremely vulnerable to severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection with high rates of hospitalization and mortality rates. In January 2021, the University of Virginia Dialysis Program initiated a program‐wide vaccination campaign to administer the Pfizer BioNTech messenger RNA SARS‐CoV‐2 (BNT162b2) vaccine. The aim of this study was to characterize the long‐term time‐dependent decline in humoral immunity in hemodialysis patients. Methods A prospective cohort study measuring serial monthly semiquantitative IgG antibody levels to the SARS‐CoV‐2 spike protein receptor binding domain in fully vaccinated in‐center hemodialysis patients. Samples were collected monthly and tested for anti‐SARS‐CoV‐2 antibodies against the anti‐spike S1 domain for 2–6 months post full vaccination. Results were presented as internationally harmonized binding antibody units (BAU/ml). To analyze the change in antibody levels over time, a linear mixed model with random intercept and random slope was used for longitudinal antibody levels. A multivariable model was used to estimate the slope of antibody levels by adjusting for selected patient characteristics. Based on the estimated intercepts and slopes for each subject from the unadjusted model, 10‐month antibody levels were projected. Results The mean baseline antibody level was 647.59 BAU/ml and 87.88% (29/33) of patients were considered qualitatively positive. Two patients were negative at baseline and an additional two had borderline results. Patient antibody levels declined at an adjusted average rate of 31% per month. At 6 months postvaccination, 40% of patients remaining in the cohort possessed either negative or borderline IgG antibody levels. Projecting future antibody levels suggests that 65% of the cohort will progress to borderline or negative antibody levels at 10 months post full vaccination. Conclusion The long‐term vaccine response following vaccination with the BNT162b2 in hemodialysis patients was characterized. Our data add to the limited pool of data in this patient population and emphasize the critical need for vaccine boosters.

while impressive, remain lower than those observed in the general population. Dialysis patients also attain lower antibody levels in response to messenger RNA vaccines compared to healthy controls. 7 Despite the majority of dialysis patients attaining a positive antibody response, the strength and long-term durability of humoral immunity following coronavirus disease 2019 (COVID-19) vaccine regimens is incompletely understood.
In January 2021, the University of Virginia began a program-wide vaccination campaign for dialysis patients exclusively using BNT162b2 (courtesy of the Virginia Department of Health) and achieved an 80% vaccination rate among prevalent dialysis patients. 8 From this cohort, a subset of patients was selected to prospectively study serial antibody levels from 2 to 6 months following full vaccination. Here, the results of serial monthly antibody levels, slope of antibody decline, and qualitative population loss of detectable humoral antibody response in this selected subset are reported.

| Study population
Sixty-nine patients undergoing in-center hemodialysis were confirmed as fully vaccinated at the sole University of Virginia study site/ dialysis center. Of these, 35 adults (>18 years) were enrolled in this study. The sample size was based on pragmatic considerations of sample volume processing capacity. All participants received two doses of the BNT162b2 vaccine between January and February 2021. Patients dialyzing for acute kidney injury and those with active infection or suspected SARS-CoV-2 infection requiring isolation were excluded at enrollment (Supporting Information: Figure 1).

| Sample collection and assessment
Samples were obtained on a monthly basis beginning at a mean of 9.1 weeks post full vaccination (defined as >14 days following second immunization) on designated collection dates for each dialysis shift (Monday-Wednesday-Friday or Tuesday-Thursday-Saturday). A 10 ml EDTA tube was collected from each patient's dialysis blood line during dialysis treatment, stored in a designated research refrigerator, and processed within 8 h of initial collection. Tubes were centrifuged at 3000 rpm (1620 rcf) for 10 min in the swing bucket rotor (S4180) at 4°C using a Beckman GS-15R centrifuge.
Plasma obtained was stored at −80°C in 0.5 ml aliquots until further analysis.
All monthly EDTA plasma samples were tested for anti-SARS-CoV-2 antibodies against the anti-spike S1 domain using the commercially available Anti-SARS-CoV-2 QuantiVac ELISA (IgG) from Euroimmun (EUROIMMUN US, Inc.). Assays were run and results were interpreted as per the manufacturer's guidelines. Samples above detection limits were rerun with further dilution (1:5 or 1:10) in the sample buffer as recommended by the manufacturer. Based on the manufacturer's recommendation, the final test results were presented as the internationally harmonized binding antibody units (BAU/ml). 9 BAU/ml was obtained by multiplying the relative unit (RU/ml) by a factor of 3.2. Final test results were considered negative for BAU/ml (<25.6), borderline for BAU/ml (≥25.6 and <35.2), and positive for BAU/ml (≥35.2). 9 To assess for undiagnosed prior infection and confirm reported histories of prior infection, the Bio-Rad Platelia SARS-CoV-2 Total Ab assay (Bio-Rad Laboratories, Inc.) was used for the qualitative detection of total antibodies (IgM/IgG/IgA) to SARS-CoV-2 nucleocapsid protein. Testing was run from EDTA plasma and limited to each patient's initial sample only. Recombinant SARS nucleocapsid protein is used in the assay to capture total antibodies in a one-step antigen capture format, followed by detection.

| Data collection
Demographic data including age, sex, race/ethnicity, and body mass index (BMI) and clinical data, including comorbidities, use of immune suppressive medication, history of malignancy, and history of transplantation were obtained from the Electronic Health Record (Table 1). Clinical information including dialysis vintage was obtained from the dialysis-specific electronic medical record system. The mean age was 62.0 years; 51.43% were women and 60% were African    Based on the antibody level cutoffs provided by the manufacturer at 6 months post full immunization (positive, borderline, and negative), 61% (17/28) of patients maintained positive antibody levels, while 39% (11/28) had borderline or negative antibody levels ( Figure 2). Additionally, the prediction of antibody level at month 10 post full vaccination demonstrated that more than 65% of the study population is anticipated to progress to borderline or negative antibody status (Figure 1).

| DISCUSSION
The goal of the study was to define long-term SARS-CoV-2 spike protein antibody response decay curves in a cohort of early- The study has limitations, which may limit generalizability.
Notably, this was a small sample size and a nonrepresentative In conclusion, long-term IgG spike protein antibody decline rates in response to vaccination with BNT162b2 were determined.
The declining antibody levels suggest that dialysis patients vaccinated with BNT162b2 will greatly benefit from receipt of a booster dose.

CONFLICT OF INTEREST
The authors declare no conflict of interest.

DATA AVAILABILITY STATEMENT
The data set used for this analysis is not publicly available. The data utilized was obtained from the Electronic Health Record and from the dialysis-specific electronic medical record system, which is restricted to use by only authorized employees.

ETHICS STATEMENT
This research proposal was reviewed and approved by the University of Virginia Institutional Review Board for Health Sciences Research (tracking number: HSR 210095).

TRANSPARENCY STATEMENT
The lead author Eibhlin Goggins affirms that this manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.